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Old 05-05-2017, 05:36 PM
astro744
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astro744 is offline
 
Join Date: Apr 2007
Posts: 1,244
Grazing occultations are much more fun and scientifically useful if done right but you have to be prepared for a drive to position yourself in the right path. It's been a very long time since I did my last one but I still remember it as if it was yesterday. The star was Antares and it was -8 deg at 1am in Bomballa, NSW and the whole event only took about a minute or so plus the 6 hour round trip including time to find the correct site for this particular graze for me. Multiple observers are best, the more the better as this enables a closer spacing which determines the resolution of the data. Observers are spaced at approx equal distances along the path such that some see two events and some none and those in between see multiple events because of the peaks and valleys on the limb of the Moon. The most exciting thing with Antares is is that it is a double star and it is possible for one star to be eclipsed by the limb of the Moon but not the other so what you see is a gradual brightness drop or even a sustained brightness drop if one star is behind a flat part of the limb for a sustained length of time. I witnessed this and it was spectacular.

All you needed back then was a telescope with tracking, a shortwave radio tuned to a time signal and a tape recorder. You then later play back the tape and try and determine to 0.1 sec accuracy the time of each event. I think these days high sensitive video cameras are used combined with a GPS unit the imprints that time signal onto the video and this is far more accurate.

If anyone's is interested ask your local astronomical society if they have a graze coordinator and see what events are coming up. They are a lot of fun but be prepared to travel. Note that most grazes are of dimmer stars but these can still be quite good if favourable and by that I mean the star grazes the dark part of the limb and is easy to see.
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